In the past, as a method for measuring the resistivity of a silicon single crystal wafer, a method for measuring C-V (capacitance-voltage) characteristics has been known. To measure the C-V characteristics, a Schottky junction is formed on the surface of a silicon single crystal wafer which is a sample, and a depletion layer is increased in the silicon single crystal wafer by application of a reverse bias voltage with the reverse bias voltage being continuously varied, whereby the capacity is varied. To form the Schottky junction on the surface of the silicon single crystal wafer, a mercury electrode, for example, is used.
When the silicon single crystal wafer which is a sample has an n-type region on the surface thereof (such as an n-type substrate and a wafer having an n-type epitaxial layer on the surface thereof), the surface of the wafer is oxidized in advance to form a thin silicon oxide film and a mercury electrode is joined onto the silicon oxide film, whereby it is possible to measure the C-V characteristics.
As the forming a thin silicon oxide film on a silicon single crystal wafer surface, a method by which a wafer is immersed in a solution containing an oxidizer such as hydrogen peroxide for a few minutes and then rinsing and drying are performed is known (Nonpatent Literature 1). However, in this method, since it takes about 20 minutes to perform from oxidation processing to drying, it is necessary to shorten the amount of time.
Thus, a method by which the surface of a wafer is oxidized by ozone gas by exposing a silicon single crystal wafer to ultraviolet light in an atmosphere containing oxygen is proposed (Patent Literature 1).